It is known to control the phase of operation of a motor by utilizing a digital phase controller which, by means of a counter, generates a phase control signal. counter is started by a phase reference pulse, and operated at a clock frequency which is higher, and preferably substantially higher than the repetition frequency of the phase reference pulses. The motor to be controlled provides, for example by means of an opto-electronic pulse transducer, a scanning pulse which is representative of the actual value of the phase position. The count state which occurs in the counter after the phase reference pulse until the scanning pulse occurs is a value for the phase difference between the scanning pulse from the motor and the phase reference pulse. This count state, then, can be used, as known, to control the operation of the motor.
A control system of this type should reach stable state as quickly as possible. To obtain prompt locking-on or latching of such a control system, it is important to determine the phase difference within a major portion of the cycling time of the sequence of the phase reference pulses. This means that the counter, which is started by the phase reference pulses should reach its maximum count state only shortly before the subsequent phase reference counting pulse. For precise phase control of the motor,then, counters with correspondingly high count capacity are needed. For example, utilizing an 8-bit counter, permits an accuracy of phase control of 1/256th of the cycling time. Such an accuracy is suitable for some applications, but not for many others. To control the operation of the head wheel of a video tape recorder apparatus, for example, the accuracy is insufficient; substantially higher phase control accuracy is required.